The present invention relates to an ion mobility spectrometer, a mass spectrometer, a method of ion mobility spectrometry and a method of mass spectrometry.
Mass spectrometers are known which comprise an ion mobility spectrometer stage which is operated at sub-ambient pressure within a vacuum chamber of the mass spectrometer. The ion mobility spectrometer stage is operated at a gas pressure in the range 0.1 to 10 mbar and is located in a differentially pumped vacuum chamber in order to minimise gas loading of other ion-optical components and in particular the mass analyser which forms the final stage of the mass spectrometer. Ions are accumulated in an ion trap which is arranged upstream of the ion mobility spectrometer stage. The ion trap is maintained at a relatively low pressure and hence it is necessary to drive ions from the ion trap into the ion mobility spectrometer stage against a significant outflow of gas from the ion mobility spectrometer stage. The significant outflow of gas from the ion mobility spectrometer stage can be particularly problematic as the use of inappropriate electric fields to drive ions out of the ion trap and into the ion mobility spectrometer stage can cause fragile ions to fragment.
It is therefore desired to provide an improved mass spectrometer.